THERMAL BIOLOGY OF ZOO-HOUSED CHELONOIDIS CHILENSIS: DETERMINING THE ACTIVITY PATTERN AND ESTIMATING SELECTED AND CRITICAL MAXIMUM TEMPERATURE

Ectothermic animals depend on environmental temperature to regulate their body temperature. The Chaco Tortoise (Chelonoidis chilensis) is widespread in South America; however, populations are threatened mainly because of the pet trade. We described the activity pattern of C. chilensis relative to environmental temperature under semi-natural conditions in a zoo enclosure. We also estimated thermal parameters under controlled laboratory conditions: selected temperature (T-sel) and critical maximum temperature (CTmax) between sex and size indicators. In the enclosure, 81% of the observations were from inactive tortoises and 19% from active tortoises. Tortoises were active over a wide thermal range (12.0 degrees-38.0 degrees C) and T-sel was 34.4 degrees +/- 0.3 degrees C (mean +/- standard error), with no significant differences among sizes or between sexes. Heavier tortoises spent significantly more time at the lowest temperature than lighter ones. The range of CTmax was 36.3 degrees-42.0 degrees C and this parameter was inversely related to tortoise length but did not differ between sexes. The results suggest a wide thermal range in C. chilensis, dependence of thermal behavior on body size but not on sex, and a wider range of body temperatures in smaller individuals than in larger ones. Knowing the parameters that influence thermoregulation contributes to the improvement of management strategies under semi-natural conditions, which, in turn, can be extrapolated to wild populations.